The present disclosure relates to motor-compressor units, comprising an electric motor and a compressor driven by the electric motor, housed in a pressure casing. Embodiments disclosed herein specifically relate to motor-compressor units for subsea applications. More specifically, the disclosure relates to improvements to motor-compressor units comprising one or more magnetic bearings supporting the driving shaft, which connects the motor and the compressor.
Motor-compressor units are usually comprised of an outer pressure casing which houses an electric motor and a compressor, connected to one another by a driving shaft. The shaft is rotatingly supported in the pressure casing by a plurality of bearings. In some applications, specifically in subsea applications, the pressure casing comprises a motor compartment, which houses the electric motor, and a compressor compartment, which houses the compressor. Both compartments are sealingly closed to prevent penetration of sea water. Earlier subsea motor-compressor units usually employed oil-lubricated bearings for supporting the driving. Recently, magnetic bearings, or active magnetic bearings have been introduced in this kind of machinery, in order to avoid certain disadvantages derived from the presence of lubricating oil in the pressure casings.
Magnetic bearings are controlled by an electronic control system. The electronic control system must be connected to the magnetic bearings housed in the pressure casing. Specifically in subsea applications, a wire connection with subsea water-tight connectors electrically connect the control system with the interior of the pressure casing. The control system is placed externally of the pressure casing and at a distance therefrom. Usually the motor-compressor unit and the control system are mounted on a skid or baseplate. The housing wherein the control unit is arranged is in turn connected by means of data and power cables with electric and electronic devices place above the sea level.
These known arrangements are expensive and cumbersome. The use of a relatively large number of subsea wire connectors renders this known systems prone to failure due to water leakages inside the motor-compressor casing and/or the separate housing wherein the electronic components of the control system are arranged.
Improvements relating to the arrangement of the control system of the magnetic bearings in a motor-compressor unit would thus be desirable.